northd: Add lsp option force_fdb_lookup.

This option is applicable only if the lsp is of default 'type'
i.e. type=empty_string (which is a VM (or VIF) interface) and the
lsp also has 'unknown' addresses configured.
If lsp option 'force_fdb_lookup' is set to true, mac addresses
of the lsp (if configured) are not installed in the l2 lookup
table of the Logical Switch pipeline. However, MAC addresses
are learnt using the FDB Table.

Usecase:
=========
This option is required to reduce packet loss when VM is being
migrated across AZs (via VXLAN tunnel). lsp is configured in both
AZs on different logical switches which are sharing the same IP
subnet. If the port has unknown address set along with MAC, IP
then, any packet destined to VM's MAC on destination AZ will get
forwarded locally, which may lead to packet loss during VM migration.

This option is useful to reduce packet loss during VM migration
by forcing the logical switch to learn MAC using FDB.

The other way to address this issue is to use pkt_clone_type
option but this causes too much of packet duplication when there
are multiple ports with unknown address in the logical switch.

Signed-off-by: shibir-basak <shibir.basak@nutanix.com>
Signed-off-by: Numan Siddique <numans@ovn.org>

AUTHORS.rst

@@ -366,6 +366,7 @@ Shan Wei                           davidshan@tencent.com
 Sharon Krendel                     thekafkaf@gmail.com
 Shashank Ram                       rams@vmware.com
 Shashwat Srivastava                shashwat.srivastava@tcs.com
+Shibir-basak                       shibir.basak@nutanix.com
 Shih-Hao Li                        shihli@vmware.com
 Shu Shen                           shu.shen@radisys.com
 Simon Horman                       horms@ovn.org

NEWS

@@ -17,6 +17,9 @@ Post v24.03.0
     external-ids, the option is no longer needed as it became effectively
     "true" for all scenarios.
   - Added DHCPv4 relay support.
+  - A new LSP option "force_fdb_lookup" has been added to ensure the additional
+    MAC addresses configured on the LSP with "unknown", are learnt via the
+    OVN native FDB.
 
 OVN v24.03.0 - 01 Mar 2024
 --------------------------

northd/northd.c

@@ -1385,6 +1385,16 @@ lrport_is_enabled(const struct nbrec_logical_router_port *lrport)
     return !lrport->enabled || *lrport->enabled;
 }
 
+static bool
+lsp_force_fdb_lookup(const struct ovn_port *op)
+{
+    /* To enable FDB Table lookup on a logical switch port, it has to be
+     * of 'type' empty_string and "addresses" must have "unknown".
+     */
+    return !op->nbsp->type[0] && op->has_unknown &&
+        smap_get_bool(&op->nbsp->options, "force_fdb_lookup", false);
+}
+
 static struct ovn_port *
 ovn_port_get_peer(const struct hmap *lr_ports, struct ovn_port *op)
 {
@@ -9594,6 +9604,12 @@ build_lswitch_ip_unicast_lookup(struct ovn_port *op,
 
         if (ovs_scan(op->nbsp->addresses[i],
                     ETH_ADDR_SCAN_FMT, ETH_ADDR_SCAN_ARGS(mac))) {
+            /* Skip adding flows related to the MAC address
+             * as force FDB Lookup is enabled on the lsp.
+             */
+            if (lsp_force_fdb_lookup(op)) {
+                continue;
+            }
             ds_clear(match);
             ds_put_format(match, "eth.dst == "ETH_ADDR_FMT,
                           ETH_ADDR_ARGS(mac));

northd/ovn-northd.8.xml

@@ -2038,6 +2038,12 @@ output;
           also forwarded to the  <code>MC_UNKNOWN</code> multicast group.
         </p>
 
+        <p>
+          The above flow is not added if the logical switch port is of type
+          VIF, has <code>unknown</code> as one of its address and has the
+          option <code>options:force_fdb_lookup</code> set to true.
+        </p>
+
         <p>
           For the Ethernet address on a logical switch port of type
           <code>router</code>, when that logical switch port's

ovn-nb.xml

@@ -1269,6 +1269,17 @@
           </p>
         </column>
 
+        <column name="options" key="force_fdb_lookup"
+                type='{"type": "boolean"}'>
+          This option is supported only if the Logical Switch Port is of
+          default <ref column="type"/> (i.e. type set to empty_string) and also
+          <ref column="addresses"/> column contains <code>unknown</code>.
+          If set to <code>true</code>, MAC addresses (if configured)
+          are not installed in the l2 lookup table but the MAC addresses are
+          learnt and stored in the FDB table.
+          The default value is <code>false</code>.
+        </column>
+
         <column name="options" key="pkt_clone_type"
                 type='{"type": "string", "enum": ["set", ["mc_unknown"]]}'>
           If set to mc_unknown, packets going to this VIF get cloned to all

tests/ovn-northd.at

@@ -6972,6 +6972,44 @@ AT_CLEANUP
 ])
 
 
+OVN_FOR_EACH_NORTHD_NO_HV([
+AT_SETUP([check options: force_fdb_lookup for LSP])
+ovn_start NORTHD_TYPE
+ovn-nbctl ls-add S1
+ovn-nbctl --wait=sb lsp-add S1 S1-vm1
+ovn-nbctl --wait=sb lsp-add S1 S1-localnet
+ovn-nbctl --wait=sb lsp-set-addresses S1-vm1 "50:54:00:00:00:01 192.168.0.1" unknown
+ovn-nbctl --wait=sb lsp-set-type S1-localnet localnet
+
+#Verify the flows before setting force_fdb_lookup option
+ovn-sbctl dump-flows S1 > S1flows
+AT_CAPTURE_FILE([S1flows])
+
+AT_CHECK([grep -e "ls_in_l2_lkup.*S1-vm1" S1flows | ovn_strip_lflows], [0], [dnl
+  table=??(ls_in_l2_lkup      ), priority=50   , match=(eth.dst == 50:54:00:00:00:01), action=(outport = "S1-vm1"; output;)
+])
+
+#Set the force_fdb_lookup option and verify the flows
+ovn-nbctl --wait=sb set logical_switch_port S1-vm1 options:force_fdb_lookup=true
+ovn-nbctl --wait=sb set logical_switch_port S1-localnet options:force_fdb_lookup=true
+
+ovn-sbctl dump-flows S1 > S1flows
+AT_CAPTURE_FILE([S1flows])
+
+#Verify the flows for default port type (VM port)
+AT_CHECK([grep -e "ls_in_l2_lkup.*S1-vm1" S1flows | grep -e "match=(eth.dst == 50:54:00:00:00:01)"], [1], [])
+AT_CHECK([grep -e "ls_in_.*_fdb.*S1-vm1" S1flows | ovn_strip_lflows], [0], [dnl
+  table=??(ls_in_lookup_fdb   ), priority=100  , match=(inport == "S1-vm1"), action=(reg0[[11]] = lookup_fdb(inport, eth.src); next;)
+  table=??(ls_in_put_fdb      ), priority=100  , match=(inport == "S1-vm1" && reg0[[11]] == 0), action=(put_fdb(inport, eth.src); next;)
+])
+
+#Verify the flows for a non-default port type (localnet port)
+AT_CHECK([grep -e "ls_in_.*_fdb.*S1-localnet" S1flows], [1], [])
+
+AT_CLEANUP
+])
+
+
 OVN_FOR_EACH_NORTHD_NO_HV([
 AT_SETUP([check options:pkt_clone_type for LSP])
 ovn_start NORTHD_TYPE